Stabilization of polystyrene with n, n&#39;-di-beta-naphthyl-p-phenylenediamine



United States Patent Ofiice Patented Aug. 21, 1956 STABILIZATION OF POLYSTYRENE WITH N,N-DI- B-NAPHTHYL-P-PHENYLENEDIAMINE Ernest H. Wood, Westfield, N. J., and James R. Wilkinson,

Milwaukee, Wis., assignors to Union Carbide and Carbon Corporation, a corporation of New York No Drawing. Application May 19, 1953, Serial No. 356,101

2 Claims. (Cl. 260-453) This invention relates to compositions comprising a polystyrene resin and to the stabilization of such compositions against degradation or decomposition upon weathering and upon exposure to elevated temperatures in the presence of air.

Polystyrene has become widely known as it possesses many unique and desirable properties which lend themselves to many purposes. Although its applications are numerous and its uses extensive, there are instances in which the performance of polystyrene is not entirely satisfactory. For example, when polystyrene is exposed to elevated temperatures in the presence of air, or to normal temperatures in the presence of ultra-violet light as under conditions of outdoor use, destruction of the plastic occurs by a process known as molecular degradation. This phenomenon has the eifect of causing the individual molecules of polystyrene to crack, or depolymerize to lower polymers and results in the plastic turning yellow, becoming dull and, eventually, fine cracks and crevices develop on its surface.

Heretofore, to overcome molecular degradation or decomposition of polystyrene from the above causes, it has generally been necessary to employ two stabilizers; one of which functions to stabilize the resin against the effects of weathering or outdoor use, and the other of which functions to stabilize the resin against the eifects of elevated temperatures. This method of stabilizing polystyrene has not been entirely satisfactory and, therefore, it is an object of this invention to provide a new stabilizer which will eifectively stabilize polystyrene against molecular degradation due to either elevated temperatures, outdoor exposure, or both.

We have found that the incorporation of small amounts of N,N-di-,B-naphthyl-p-phenylenediamine in polystyrene resins effectively retards degradation, or decomposition of the polymer when subjected to either or both of the above conditions. While varying amounts of the stabilizer may be employed, we have found that from about 0.01 percent to about 10 percent by weight of polystyrene resin is particularly efiicacious. However, our preferred range varies from about 0.1 percent to about 1.0 per cent by weight of polystyrene resin. The stabilizing agent must be intimately admixed with the resin, and it has been found that the quantities of the stabilizing agent employed do not materially alter other properties of the product or detract from the value thereof in their customary use.

The stabilizer of our invention may be incorporated in polystyrene resins, or compositions thereof, by any of the well-known methods in the art. For example, this may be accomplished by film-casting wherein the stabilizer and resin are dissolved in a mutual solvent and the solvent subsequently evaporated. Or, if desired, the stabilizer may be incorporated on a conventional two-roll mill, or in Banbury mixer. In addition, the stabilizer may be added to the polystyrene resin during the course of preparation of a composition in the same manner that coloring materials are normally added.

To illustrate the beneficial aspects of our invention, specimens of polystyrene containing from to percent by weight of polystyrene resin of N,N'-di-/8-naphthyl-pphenylenediamine were subjected to elevated temperature and weathering tests. The elevated temperature test comprised exposing the specimens at 175 C. for one hour in an air-circulating oven. The weathering test comprised placing the specimens in an Atlas XIA accelerated Weather-O-Meter. Normally, weathering tests are conducted out-of-doors and involve the exposure of specimens to the sunlight as it is well-known that molecular degradation occurring during weathering is due primarily to the effects of ultraviolet light and air. Outdoor exposure of the specimens is, of necessity, time-consuming and, therefore, the weathering tests were conducted in the Weather-O-Meter which furnished conditions comparable to outdoor exposure in greatly reduced periods of time.

An efiective method for determining the molecular degradation of the polymer comprises, comparing the viscospipette and measuring the time for the same volume of a 0.1000 gram solution of polystyrene in ml. of benzene to flow between the identical index points. The relative molecular weight is then calculated from the following formula:

Relative molecular weight: 578,000(% 1) where Ts=time for polystyrene solution Tb=time for benzene The following examples more fully disclose the invention:

EXAMPLEI Specimens of polystyrene containing 0, 0.01, 0.1, 1.01, and 5.26 percent by weight of polystyrene of N,N-di-,8- naphthyl-p-phenylenediamine were prepared by dissolving the resin and stabilizer in a benzene solvent and the solvent evaporated by heating a thin layer of the solution on a glass plate, thus forming a film. The films were then broken up and compression-molded into specimens of 0.030 to 0.034 inch thickness. The specimens were then subjected to weathering conditions by exposing them for 500 hours in an Atlas XIA Weather-O-Meter. Degradation of polystyrene was measured by determining the loss of relative molecular weight of the stabilized and unstabilized specimens and by a comparison of their appearances. The following table comprises a tabulated account of the molecular weights of the various specimens before and after exposure to the Weather-O-Meter.

Table I Relative Relative Percent of Stabilizer by Weight of Molecular Molecular Polystyrene Wgt. 10- Wgt.X10-

Before After Exposure Exposure As may be readily seen from the above table, specimens of polystyrene containing the stabilizer of our invention are effectively stabilized against decomposition and against excessive loss of molecular weight caused by weathering.

EXAMPLE II Specimens containing 0, 0.01, 0.1, 1.01, and 5.26 percent by weight of polystyrene of N,N-di-,B-naphthyl-pphenylenediamine, and of 0.020 inches thickness, were prepared in the identical manner disclosed in Example I. The specimens were then subjected to an elevated temperature test conducted in an air-circulating oven at 175 C. for a period of one hour. Degradation of polystyrene was measured by determining the loss of relative molecular weight of the stabilized-and unstabilized' specimens and by acomparison of their appearance.

The following table comprises a tabulated account of the molecular weights of the specimens before and after exposure:

Table 1 Relative o ecular Wgt.X107

After Exposure Relative Molecular WgtXlD- Before E p sur Percent of Stabilizer by Weightcf Polystyrene The above examples clearly illustrate that N,N'-di-finaphthyl-p-phenylenediamine elfectively stabilizes polystyrene against molecular degradation ordinarily caused by weathering and by elevated temperatures.

It is to be understood that the stabilizer of our invention may be advantageously employed with all polystyrene resins including the well-known copolymer resins prepared by the copolymer-ization of polystyrene with other polymerizable compounds. Furthermore, our stabilizer may be effectively employed with allpolystyrene compositions prepared by the admixture of the Well-known modifying agents, such as plasticizers, pigments, fillers and dies, with polystyrene. resins and copolymer resins.

We claim:

1. A heat and light-stabilized composition of matter comprising a homopolymer of styrene and from about 0.01% to about 10% by weight of said homopolymer of N,N'-di- 3-naphthyl-p-phenylenediamine.

2. A heat and light-stabilized composition of matter comprising a homopolymer of styrene and from about 0.1% to about 1% by weight of said homopolymer of N,Ndi-fl-naphthyl-p-phenylenediamine.

References Cited. in the file of this patent UNITED STATES PATENTS 2,529,060 Trillich Nov. 7, 1950 

1. A HEAT AND LIGHT-STABILIZED COMPOSITION OF MATTER COMPRISING A HOMOPOLYMER OF STYRENE AND FROM ABOUT 0.01% TO ABOUT 10% BY WEIGHT OF SAID HOMOPOLYMER OF N,N''-DI-B-NAPHTHYL-P-PHENYLENEDIAMINE. 